TRACE-METAL BEHAVIOR DURING SUMMER IN A STRATIFIED MEDITERRANEAN SYSTEM - THE LOUROS ESTUARY (GREECE)

Trace metals (Al, Pb, Zn, Cr, Cu, Ni, Fe, Mn) were studied in waters ( dissolved and particulate phases) and sediments of the Louros Estuary in the Amvrakikos Gulf, one of the most important European wetlands lo cated at the NW coast of Greece. The study system is small, with a rel atively narrow mixing zone, typical for Mediterranean estuaries. Parti cular emphasis was given to understanding the conditions prevailing in summer. During this season saline water intrudes the estuary along th e river bed, despite the existing shallow sill, and forms a thin salt- wedge water mass, which occupies the near bottom layer with its thin e nd pointed upstream. Particulate metal concentrations within this sali ne bottom layer are considerably higher than in the riverine and marin e sections of the estuary. Since the metal content of particles collec ted upstream is higher than that of the marine ones, there is a clear evidence that the salt-wedge acts as a 'sink' for most metals during t he summer. Coexistance in the same zone of high dissolved metal concen trations indicate that loosely associated metals are desorbed from riv erine particles, whereas newly formed suspended matter is deposited to gether with particles, transported by the river. The accumulation of m etals in the near bottom layer affects directly their distribution in the sediments. The maximum concentrations of the metal fraction which is loosely held in sediments, are found primarily at the same site. Th e distribution of the 'non-labile' metal fraction of the sediments (pa rticularly for Cu and Pb) is broadly constant throughout the estuary, confirming the absence of any significant natural or industrial point sources, at the lower part of the river. However, the analysis of sedi ment cores reveals an enrichment of this metal fraction at the top, ne ar surface sections of the mouth area, indicating relatively recent po llution.